I just never got into IRC that much-- I'm usually flipping thru the site from the office, so it can be difficult to get into an extended conversation (I dunno, they expect me to work or something ) Also, I type dead slow, so I'm usually 3-4 comments behind in a live chat.
If you add it into the new site design, I wouldn't build it as a popup window. Integrated would look better, and you wouldn't lose the window behind other apps.
Looking forward to the new design